Powder inhaler devices are well known in the state of the art. Some of those devices include a single reservoir containing several doses of powder, and metering means that are adapted to take, on each actuation, one dose of powder for expulsion to the user. Other devices provide individual predosed reservoirs, e.g. blisters, each containing a single dose of powder, each reservoir being opened individually during actuation so as to make it possible to expel the powder contained therein. In the context of a device with one or more predosed reservoirs, different solutions have been proposed for opening the reservoir and accessing its content so as to enable it to be expelled. Thus, it has been proposed to make predosed reservoirs with a peel-off layer, making it possible to expose the reservoir and its powder to a flow of gas, in general air, in order to expel the dose. Other devices provide piercer means for piercing or tearing a portion of the reservoir, thereby also making it possible to expel the content thereof. A problem that can occur with such devices relates to the risk of losing some or all of the doses after opening the reservoir and before inhalation. This reduces metering accuracy and dose reproducibility (underdosing). Another even more serious problem relates to the risk of overdosing. For example, this can occur if, in a device having predosed reservoirs, a reservoir is opened, but the appliance is not used, such that the content of the reservoir is not inhaled. In this event, if the powder is likely to escape from the reservoir and become deposited in portions of the device, then during the next actuation, which will cause another reservoir to open, there is a risk of overdosing. The powder that escaped from the first reservoir could be expelled together with the complete dose from the second reservoir. Depending on the kind of powder, which can be a pharmaceutical, such overdosing risks being very harmful to the user. Another problem that occurs with powder inhaler devices relates to the accuracy and the reproducibility of the metered dose. It can happen that the reservoir or the metering system is not always to be emptied completely on each actuation, thereby generating risks of metering differences from one dose to another, and thus of losing accuracy and reproducibility for the metered dose.